This invention relates to controls for electrically powered windshield wiper systems for use on motor vehicles and particularly for such systems in which the wiper blades have partially overlapping patterns and a symmetrical overlap park position. In addition, it relates to such systems using separate motors for the wiper blades with consequent need for coordinating such motors to prevent interference between the wiper blades in operation and parking.
The prior art shows a number of windshield wiper controls which control separate wiper motors. The Gumbert U.S. Pat. No. 3,721,878, issued Mar. 20, 1973 shows such a system with a switching arrangement in which each wiper motor is powered only during a certain angular range of the other wiper blade. However, in the Gumbert system, the blades are parked at the sides of the windshield in the outer wipe positions; and, after one starts by moving across the windshield toward the other, they move in a tandem pattern until the system is turned off, at which time they move back to the side park positions again. The Gumbert system does not teach how to control an opposing wipe with partial overlap and an overlap park position at the bottom of the windshield.
An additional prior art system is that shown in UK patent application GB No. 2 132 793, published July 11, 1984. In this system, wipers in a standard tandem pattern with standard park position but with separate drive motors are coordinated through a switching arrangement whereby each wiper must proceed to a predetermined angle in order that the other be driven through a predetermined angle, the angles being so arranged to prevent blade interference. A similar arrangement is suggested in a digital computer embodiment, although not described in detail, in column 10, lines 29-41 of the Carpenter et al U.S. Pat. No. 4,431,954, issued Feb. 4, 1984 (filed Nov. 26, 1982). The Carpenter et al patent shows a storm pattern for a dual motor wiper system which otherwise produces a standard tandem pattern with overlapping park. In the storm pattern, the driver's side blade stops at outerwipe to allow the other blade to descend to the bottom of the windshield and back and thus provide wiping of an area in front of the driver four times in each complete cycle rather than the normal two times. However, neither the UK application nor Carpenter et al show a control for an opposing, overlapping wiper pattern.